Things are hotting up. Hours after the traditional British election egg was thrown at David Cameron's shoulder, we learned this morning that James Murdoch and his enforcer, Rebekah Brooks, nee Wade, burst their way into the offices of the Independent to give executives a hard time.

Gosh, that's pretty uncool, and may suggest that expensive suits at News International are rattled by Cleggmania, which could leave them out in the cold if the Tories fail to win on 6 May.

What seems to have upset them are ads that the Indy has been running along the lines of "Rupert Murdoch won't decide this election – you will." Brooks apparently rang Simon Kelner, the editor-in-chief and now chief executive of the Indy to complain that dog does not eat dog in Fleet Street.

That means that editors and owners do not attack each other in person – not their politics, their finances or their private lives. Remember the running battle, later patched up, between the Daily Mail and the once-mighty Daily Express over the former's habit of referring (correctly) to Express owner Richard Desmond as a pornographer? That sort of thing.

Anyway, it's fun, not least because Freud Communications did the Indy's redesign. And who is Matthew Freud married to? Why, to James's less impetuous sister, Elisabeth Murdoch. Small world, eh?

Anyway, the Brooks-Murdoch posse turned up at the Indy's HQ – now housed in the Mail's London premises, the old Derry and Toms department store in Kensington High Street, got past security and appeared unannounced and uninvited on the editorial floor.

"They barged in and Kelner had to take them into an office where discussions took place. Rebekah was observed in gesticulating mode," says my source. The incident was mentioned on Radio 4's Today programme, where Trevor Kavanagh, a Sun guru, was found to be unbriefed about the whole thing.

Lively times. As noted here yesterday, and articulated forcefully in this week's Guardian by David Yelland, an ex-Sun editor, the Murdoch empire may be badly caught out if David Cameron does not become prime minister. Don't these people know that I still think he will?

Never mind. The "Kill Klegg" bandwagon gathers pace this morning, as we all knew it would. All the day's fresh allegations end up in later editions of the Mail, which has a very efficient news Hoover. Thus:

• He is guilty of a "Nazi slur," says the Mail, because in 2002 he wrote on the Guardian website that the British now have more of a problem than the repentant and prosperous Germans because of lingering "delusions of grandeur".

Mike's verdict: Oh p-u-u-l-eeese, if the Mail can't smear him better than that it might as well hand the job over to the usually-inferior Telegraph.

• Talking of which, as the Guardian reports, the Telegraph has dug up an odd story about how Lib Dem donors paid regular £250 payments into Clegg's own bank account, apparently to pay a researcher. Clegg says it was all declared.

Mike's verdict: That's a bit better than the Mail's yarn.

• Among other charges in the Mail today is that Clegg had TV coaching for the big debates; that Lib Dem candidates say nasty things about rival candidates and project different policies to different target audiences; that officials of the party gave their MPs advice on how to maximise expenses claims; that Vince Cable's plan to curb tax avoidance is optimistic according to experts; and that Clegg himself got a bit shirty yesterday.

Mike's verdict: That all sounds like a political party at work to me.

The interesting question is whether any of this mud sticks or whether voters decide that it's them, not Rupert Murdoch or the Mail's own editor – Paul Dacre – who decides the election.